df <- data.frame(x = c("1", "2", "3", "4", "5"), 
                 y = c("1", "1", "1", "1", "1")) 

# create steps for slider
steps <- list(
  list(args = list("marker.color", "red"), 
                    label = "Red", 
                    method = "restyle", 
                    value = "1"
                    ),
  list(args = list("marker.color", "green"), 
                    label = "Green", 
                    method = "restyle", 
                    value = "2"
                    ),
  list(args = list("marker.color", "blue"), 
                    label = "Blue", 
                    method = "restyle", 
                    value = "3"
                    )
  )

fig<- df 
fig <- fig %>% plot_ly(x = ~x, y = ~y,
          mode = "markers", 
          marker = list(size = 20,
                        color = 'green'), 
          type = "scatter") 
fig <- fig %>% layout(title = "Basic Slider",
         sliders = list(
           list(
             active = 1, 
             currentvalue = list(prefix = "Color: "), 
             pad = list(t = 60), 
             steps = steps))) 

fig